Garments such as tee shirts are decorated using multi printing head, screen printing machines. The number of heads correspond to the number of colours to be printed. U.S. Pat. No. 3,795,189 [Jaffa] and U.S. Pat. No. 5,031,527 [Eppinger] disclose examples of the type of machines used in printing garments.
The garments are supported on a pallet, which in turn is supported, for registry with the printing head, on a pallet arm. The pallet is moved successively past the desired number of printing heads until the printing is complete. Different size garments require correspondingly different sized pallets. Usually pallets are of the same length but vary in width from a garment sleeve width to a large body width. The positioning of the pallet on its pallet arm needs to be precise and secure to ensure that registration with successive printing heads is maintained. Also important to the quality of printing is the off contact adjustment. The off contact distance is the gap between the screen surface and the garment. To ensure that the screen will peel off the garment this distance has to be adjusted to account for garment thickness, material and ink viscosity and type. The off contact distance is adjustable for all pallets relative to all printing heads and some machines have a central off contact control that adjusts all print heads to be the same distance from the pallet arms. However individual adjustment for each individual print head relative to each pallet is also needed.
Conventionally the individual adjustment of the screen off contact is made by adjusting the screen holding frame relative to the print head arm. The screen holder frame was connected to the print frame by screw threaded shafts passing through holes in the holder frame and having a pair of threaded nuts on said shaft on either side of said frame. The spacing of the holder frame from the print arm was adjusted by turning the pair of nuts in opposite directions to move the holder frame along the shaft toward or away from the print arm. There are four such shafts at each corner of the screen holder frame. The adjustment of the two nuts required manual dexterity and the skill of the machine operator was important in achieving accurate off contact adjustment at all locations on the screen.
U.S. Pat. No. 5,787,805 discloses the use of electrically driven stepper motors at each corner of the screen holder frame to make measurable off contact adjustments for each print head. Although this arrangement makes electronic control of off contact adjustment possible it is an expensive solution to the problem and the operator does not have direct manual control over the adjustment at the screen holder but must check the screen and then return to the control panel, detracting from operator convenience.
U.S. Pat. No. 5,765,476 discloses a set up frame having 4 threaded shafts extending through the side members of the frame to project below it and contact the pallet. This set up frame is used to obtain a uniform off contact distance for all printing heads relative to all pallets. This arrangement does not cater for individual print head adjustment.
It is an object of this invention to provide a simple inexpensive and user friendly screen off contact arrangement.